2) A non-metallic element
3) Atomic no. is 34
4) atomic weight 78.96
5) melting point (of gray selenium) 217°C
6) boiling point (gray) 684.9°C
7) amorphous 4.28 g/cm
8) gray 4.79 g/cm
9) Valence cell contains two, four, or six electrons
10) exists in the oxidation states of -2, +4, and +6
11) Shells are 1s 2s 2p 3s 3p 3d 4s 4p
12) Selenium exists in several different forms, including amorphous (noncrystalline), which is red when in powder form and black when in vitreous (glassy) form;
13) the red crystalline; and the gray metallic, which is also crystalline are two other forms
14) the metallic form is the most stable under ordinary conditions; the other forms very slowly convert to the metallic form at room temperature.
15) Has similar chemical and physical properties to sulfur and tellurium
16) Byproduct of electrolytic copper refining
17) Used in rectifiers ( A device, such as a diode, that converts alternating current to direct current) as a semi-conductor
18) Used in xerography due to the electrical conductivity of metallic selenium which increases when light strikes it and converts the light directly into electricity
19) Its photovoltaic and photoconductive actions make it useful in photocells, photographic exposure meters, and solar cells
20) Also used to make red enamels for ceramics and steel ware, as well as for the vulcanization
21) Used in rubber to increase resistance to abrasion
